Dorothy Merritts and Robert Walter, Franklin and Marshall College (dorothy.merritts@fandm.edu, robert.walter@fandm.edu)

Summary

This demonstration uses an "earthquake machine" constructed from bricks, sand paper, and a winch, to simulate the buildup of elastic strain energy prior to a seismic event and the release of that energy during an earthquake. The apparatus can be placed on a table and a simple demonstration completed in 5 to 10 minutes, although longer, more complex demonstrations can be designed as well. Substantial reference materials with an animation, photographs, diagrams, and technical specifications are available at a USGS Earthquake Hazards website, based on an earthquake machine designed by Ross Stein and demonstrated at a USGS open house.

How to set up the demonstration

Building the actual earthquake machine can take from 2 to 5 hours, depending on availability of materials and basic construction skills. The apparatus consists of a wooden board 3-4 feet in length with a winch on one end. A pulley leads from the winch to the brick and is oriented so that the force acting on the brick has no vertical component. A strip of sandpaper down half of the length of the board increases friction. Earthquake Machine Diagram and Specs provides a list of materials and a diagram of the apparatus. Photo from USGS Earthquake Model .

How to do the demonstration

The earthquake machine can be used in less than 5 minutes for a simple demonstration of how elastic energy is stored (as the winch is cranked) and then released in a sudden slip event. Cranking the winch slowly in silence is very effective, so students hear the grinding of brick upon sand paper as the slip event takes place. Alternatively, the machine can be used for a longer demonstration to illustrate the nature of recurrent slip and to explore alternative hypotheses of earthquake occurrence. Doing the demonstration in class outlines one way in which the demonstration can be used in class, along with tips for engaging students in the demonstration.

Ideas for discussing the earthquake demonstration in class

More ideas for class provides background material for topics of discussion related to the demonstration, including

three hypotheses about earthquakes that can be tested, and

background lecture material about the elastic rebound theory for the cause of earthquakes, and its relation to plate tectonics.